Dr Williams: The key questions

The pathologist accused of concealing vital evidence that would have cleared solicitor Sally Clark was at the centre of another major blunder after the death of a five-year-old girl.

Two years ago the trial of a dentist and anaesthetist accused of killing Karla Selley collapsed after Dr Alan Williams confessed under cross-examination he had made a "mistake" in not realising the significance of a heart abnormality the child had suffered from since birth.

Karla's case is just one of a series in which Dr Williams has been accused of incompetence.

She died after an operation to remove a milk tooth. The pair walked free when Dr Williams told Preston Crown Court that Karla may have died from this heart condition - not because of alleged mistakes made by dentist Michael Lane, 42, and Dr George Vanner, 67.

He admitted that as the girl's right coronary artery was not in its correct place, the undiagnosed abnormality could have made her a "ticking time bomb" liable to die at any time.

Karla, from Leyland in Lancashire, was given a general anaesthetic because she was scared of the operation but never regained consciousness.

Despite their acquittal, Dr Vanner was struck off the General Medical Register after being found guilty of serious professional misconduct in connection with Karla's case. Mr Lane was also later found guilty of serious professional misconduct by the General Dental Council, but escaped being struck off.

Dr Williams has been criticised in two other cases. Three years ago a judge ordered a jury at Chester Crown Court to acquit a mother charged with murdering her baby after criticism that Dr Williams changed his evidence.

In another case the doctor gave evidence that a man had died from being given the wrong drugs, but a second pathologist said he had found evidence that death could have been caused by a heart abnormality.

The connection between Karla's case and that of Sally Clark was highlighted by the solicitor's former MP Martin Bell. He lodged a complaint with the General Medical Council in connection with the controversial evidence submitted by both Dr Williams and a second Home Office pathologist Professor Michael Green.

The prosecution in the case had been based on the medical evidence the two men provided that allegedly confirmed she had killed her two babies.

It was when the GMC was alerted to Dr Williams's connection to Karla's case that they agreed to consider investigating the evidence submitted during the Clark trial.

The case has been referred to the Preliminary Proceedings Committee, which will decide whether there should be a full hearing. A GMC spokesman said today: "When cases are in process of being looked at we cannot comment. We're aware of the complaint and we are considering what action to take next."

The Foundation for the Study of Infant Deaths has now launched a national campaign, demanding that only specialist, paediatric pathologists should conduct post mortems on babies who have died suddenly. Sarah Kenyon of the FSID said: "Babies' bodies are very different from those of adults and in cases such as a sudden death, it can be very difficult to pinpoint the exact cause."